Electrical power conversion systems have been of concern since the advent of electricity. It has been a greater concern since the advent of commercial transmission of electrical power. Electrical power is usually transmitted in the form of alternating current (AC) at a frequency of 60 Hz and 110-120 Volts (rms) in the United States, or 50 Hz and 220 Volts (rms) in many other countries. Many appliances run directly off of the supplied voltage, such as light bulbs, toasters, motors, and the like.
Many appliances require conversion to a different voltage form in order to operate. For example, 5 Volts and 12 Volts direct current (DC) is required for operation of personal computers. Microwave ovens use 5 Volts DC and higher voltages to run the microwave tube. Television sets require 10,000-50,000 Volts DC. In order to convert the power supplied by a source into a usable form to operate many modern appliances, a variety of voltage conversion circuits are employed.
Because of the widespread demand for lower voltage operating devices, there has been some attention focused on distributing electrical power at or near the required voltage. Further, as numerous appliances in the home or office require low voltage, DC electrical power, it has been observed that the power conversion efficiencies of many devices are particularly low. In addition, it has been observed that conversion to a required voltage form can be more efficiently achieved at a central location than it can be at numerous remote locations. Distribution of low voltage electrical power can then be efficiently accomplished.
Attempts to solve power transmission problems and achieve greater efficiency include U.S. Pat. No. 4,751,398 issued to Ertz. Ertz describes a lighting system which converts 2 or 3 phase alternating current input to a direct current output. The direct current output is then distributed to several fluorescent lamp ballasts, which in turn drive fluorescent lamps. In addition, a battery backup system provides a DC power source to the fluorescent lamp ballasts in the event of AC power failure. While the AC power is operating, a battery charger maintains the power level of the battery.
U.S. Pat. No. 4,719,550 issued to Powell discloses a power conversion system dedicated to providing an uninterruptable power supply.
U.S. Pat. No. 4,590,546 issued to Maile discloses a circuit for providing a regulated DC voltage output from a wide range of AC inputs. The circuit relies on a voltage doubler to boost a low AC input level, and a full wave rectifier when the AC voltage is higher.
U.S. Pat. No. 4,538,073 issued to Freige discloses a power distribution system for use in desk top computers. The system provides a DC voltage to a number of remote modules which then regulate the voltage down to the required voltage level. Each of the remote modules are preselected for either 5 Volt or 12 Volt operation. All of the remote modules are driven by a common 33 kiloHertz (kHz) signal generator to force all of the remote modules to operate in unison and prevent feedback.
U.S. Pat. No. 4,961,130 issued to Kirchberg describes a pulse width modulation invertor which is intended to accommodate harmonic distortion through the use of "quick" or fast Fourier transforms.